JP7277634B2 - Broadband satellite communication system using optical feeder links - Google Patents

Description

TECHNICAL FIELD The disclosed technology relates to broadband satellite communication system links, and more particularly to satellites using optical links for broadband communication between satellite access nodes and satellites.

Satellite communication systems provide the means by which data, including audio, video, and various other types of data, can be communicated from one location to another. The use of such satellite communication systems has become prevalent as the demand for broadband communications has increased. Correspondingly, there is a growing demand for greater capacity on each satellite.

In satellite systems, information originates from an earth station (in some cases a ground station, but could also be an air station, a sea station, etc.), referred to herein as a satellite access node (SAN), and is transmitted to a satellite. be done. In some embodiments the satellite is a geostationary satellite. A geostationary satellite has an orbit that is synchronous with the rotation of the earth so that the satellite remains essentially stationary with respect to the earth. Alternatively, the satellite is in orbit around the earth such that as the satellite moves along its orbital path, the footprint of the satellite moves over the surface of the earth.

Information received by the satellite is retransmitted to the user beam coverage area on the ground and received by a second earth station (such as a user terminal). Communication can be unidirectional (e.g., SAN to user terminal) or bidirectional (i.e., originating at both SAN and user terminal and traversing a path to the other via satellite). can be either Possibility of increasing system capacity by providing a relatively large number of SANs and spot beams and establishing frequency reuse plans that allow satellites to communicate with several different SANs on the same frequency. There is A user spot beam is an antenna pattern that directs a signal to a specific user coverage area (e.g., a multibeam antenna with multiple feeds illuminating a common reflector, each feeding a different spot beam). generate). However, building and maintaining each SAN is expensive. Therefore, it is desirable to find a technology that can provide high capacity with a small number of such SANs.

Moreover, as the capacity of satellite communication systems increases, various problems arise. For example, while spot beams allow for increased frequency reuse (and thus increased capacity), spot beams do not provide a good match to the actual demand for capacity, and some spot beams are over-reserved. and other spot beams may be under-reserved. Increased capacity also tends to result in increased demand for feeder link bandwidth. On the other hand, the bandwidth allocated to feeder links may reduce the bandwidth available to customer links. Accordingly, improved techniques for providing high capacity broadband satellite systems are desired.

The disclosed technology is described in accordance with one or more of the various embodiments and with reference to the following figures. The drawings are provided for purposes of illustration only and represent merely examples of some embodiments of the disclosed technology. These drawings are provided to facilitate the reader's understanding of the disclosed technology. These drawings should not be considered as limiting the breadth, scope, or applicability of the claimed invention. Note that these drawings are not necessarily to scale for clarity and ease of illustration.

An embodiment of a satellite communication system that uses radio frequency signals to communicate with satellites and has a relatively large number of satellite access nodes (“SANs”, also called “gateways”) to create a high capacity system. is an explanatory diagram of .

1 is an illustration of a simplified satellite communicating with a SAN using RF signals; FIG.

1 is a simplified illustration of an embodiment of a repeater used on a forward link; FIG.

1 is a simplified schematic diagram of an example of a first of three system architectures in which optical links are used to communicate over feeder links; FIG.

4 shows an example of the relationship between IF signals, optical channels, and optical bands used by the system in some embodiments.

Fig. 2 shows an embodiment of an optical transmitter used to optically modulate a binary data stream onto an optical signal;

FIG. 5 is an illustration of an embodiment of the return path of the system of FIG. 4;

FIG. 4 is a simplified schematic diagram of a third system architecture embodiment in which an optical link is used to communicate over the feeder link;

9 is an illustration of an example relationship between subchannels, carriers, and optical signals within the system of FIG. 8; FIG.

1 is a simplified illustration of an embodiment of a SAN; FIG.

9 is an illustration of an embodiment of a return link of the system of FIG. 8; FIG.

1 is a simplified schematic diagram of an example system architecture in which satellites have on-board beamforming; FIG.

FIG. 4 is a simplified block diagram of an embodiment of a weighting/combiner module;

1 is a simplified schematic diagram of an example system architecture in which an optical signal is RF modulated in a SAN and transmitted to a satellite with onboard beamforming capability; FIG.

1 is an illustration of an example forward link of a satellite communication system using terrestrial beamforming and including an optical forward uplink and a radio frequency forward downlink; FIG.

1 is an embodiment of a forward beamformer for use in a system with terrestrial beamforming;

Example of return link components in exemplary FIG. 18, which is a simplified illustration of satellite components used to receive and transmit forward links of an exemplary system using terrestrial beamforming It is a more detailed explanatory diagram of.

Figure 3 shows an example of satellite components in detail.

FIG. 4 is an illustration of an example of a user beam coverage area formed over the continental United States;

FIG. 4 is an illustration of an embodiment of an optical transmitter having a timing module for adjusting the timing of beam element signals and timing pilot signals;

A system in which each of the K forward beam input signals contains S 500 MHz wide subchannels.

1 is a simplified block diagram of an embodiment of a beamformer; FIG.

FIG. 2 is an explanatory diagram of an embodiment of a SAN;

FIG. 4 is an illustration of an example return link for a system with terrestrial beamforming;

FIG. 4 is an illustration of one embodiment of the SAN in the return link;

FIG. 4 is an example illustration of an exemplary return beamformer;

The drawings are not intended to be exhaustive or to limit the claimed invention to the particular forms disclosed. It should be understood that the disclosed technology is subject to modifications and variations and that the present invention is to be limited only by the claims and their equivalents.

First, we discuss systems that use radio frequency (RF) communication links between satellite access nodes (SANs) and satellites. Following this introduction, we discuss some optical transmission techniques for broadband capacity satellites. After an introductory discussion of systems with optical feeder links, three techniques for modulating signals on optical feeder links are discussed. In addition, we provide three architectures for implementing these techniques.

FIG. 1 illustrates that a relatively large number of earth stations (referred to herein as "SANs" but sometimes also referred to as "gateways") 102 are feeder links to create a system 100 of relatively high capacity. 1 is an illustration of a satellite communication system 100 that communicates with satellites 104 using RF signals on both the and user links. FIG. Information is transmitted from SAN 102 via satellite 104 to a user beam coverage area where multiple user terminals 106 may reside. In some embodiments, system 100 includes thousands of user terminals 106 . In some such embodiments, each of SANs 102 is capable of establishing feeder uplinks 108 to satellites 104 and receiving feeder downlinks 110 from satellites 104 . In some embodiments, the feeder uplink 108 from SAN 102 to satellite 104 has a bandwidth of 3.5 GHz. In some embodiments, the feeder uplink signal may be modulated using 16 quadrature amplitude modulation (QAM). The use of 16QAM modulation yields a capacity of approximately 3 bits/second per hertz. By using a bandwidth of 3.5 GHz per spot beam, each spot beam can provide about 10-12 Gbps capacity. By using 88 SANs, each capable of transmitting signals of 3.5 GHz bandwidth, the system has a capacity of approximately 308 GHz bandwidth or approximately 1000 Gbps (ie, 1 Tbps).

FIG. 2 is an illustration of a simplified satellite that can be used in the system of FIG. 1, the satellite using RF signals to communicate with the SAN. FIG. 3 is a simplified illustration of a repeater 201 used on the forward link (ie, receiving the RF feeder uplink and transmitting the RF customer downlink) within the satellite of FIG. A feed 202 in a feeder link antenna (not shown) of satellite 104 receives the RF signal from SAN 102 . Although not shown in detail, the user link antenna may be one or more multibeam antenna arrays (e.g., multiple feeds illuminating a shared reflector), direct radiating feeds, or It can be in any of other suitable configurations. Also, the user link and feeder link antennas can share feeds (eg, using dual-band combined transmit, receive), reflectors, or both. In one embodiment, the feed 202 operates on two orthogonal polarizations (i.e. right hand circular polarization (RHCP) and left hand circular polarization (LHCP) or alternatively horizontal and vertical polarization). signal can be received. In one such embodiment, output 203 from one polarization (eg, RHCP) is fed to first repeater 201 . The output is coupled to the input of a low noise amplifier (LNA) 304 (see Figure 3). The output of LNA 304 is coupled to the input of diplexer 306 . A diplexer splits the signal into a first output signal 308 and a second output signal 310 . A first output signal 308 is at a first RF frequency. A second output signal 310 is at a second RF frequency. Each of the output signals 308,310 are coupled to frequency converters 312,314. A local oscillator (LO) 315 is also coupled to each of the frequency converters 312,314. A frequency converter shifts the frequency of the output signal to the user downlink transmission frequency. In some embodiments, the same LO frequency is applied to both frequency converters 312,314. The outputs of frequency converters 312,314 are coupled to hybrid 320 via channel filters 316,318. A hybrid 320 combines the outputs of the two channel filters 316 , 318 and couples the combined signal to a linearization channel amplifier 322 .

Combining the signals in hybrid 320 allows the signals to be amplified by a single traveling wave tube amplifier (TWTA) 324 . The output of linearization channel amplifier 322 is coupled to TWTA 324 . TWTA 324 amplifies the signal and couples the amplified output to the input of high pass filter and diplexer 326 . A high pass filter and diplexer 326 splits the signal based on the frequency of the original signal back into two outputs, the higher frequency signal portion being coupled to a first antenna feed 328 and the lower frequency The signal portion is coupled to a second antenna feed 330 . A first antenna feed 328 transmits a user downlink beam to a first user beam coverage area U1. A second antenna feed 330 transmits a user downlink beam to a second user beam coverage area U3.

The output 331 of the feed 202 from the second polarization (eg LHCP) is coupled to the second arm 332 of the repeater. The second arm 332 functions in a similar manner to the first 201, but the output frequencies transmitted to user beam coverage areas U2 and U4 are the same as the frequencies transmitted to user beam coverage areas U1 and U3. will be different.

In some embodiments, optical links may be used to increase the bandwidth of feeder uplinks 108 from each SAN 102 to satellites 104 and feeder downlinks 110 from satellites to each SAN 102 . This can provide a number of advantages, including making more spectrum available for customer links. Additionally, the number of SANs 102 can be reduced by increasing the bandwidth of the feeder links 108,110. Reducing the number of SANs 102 by increasing the bandwidth of each feeder link to/from each SAN 102 reduces the overall cost of the system without reducing system capacity. On the other hand, one of the problems with the use of optical transmission signals is that optical signals tend to be attenuated while passing through the atmosphere. In particular, if the sky is not clear along the path from the satellite to the SAN, the optical signal will exhibit significant propagation loss due to signal attenuation.

In addition to attenuation due to reduced visibility, scintillation occurs under adverse atmospheric conditions. As such, techniques can be used to mitigate the effects of optical signal fading due to atmospheric conditions. In particular, as discussed in more detail below, there are several satellite-mounted lenses used to receive optical signals and satellite-mounted lasers used to transmit optical signals. can be directed to one of the SANs. These SANs are scattered around the globe such that the likelihood of exhibiting atmospheric adverse conditions is high at different times (i.e., the likelihood of fading occurring on the path between a satellite and a particular SAN). When is high, fading is relatively less likely on the path between the satellite and each of the other SANs).

By taking into account differences in atmospheric conditions in different regions of the country, when the atmosphere between a satellite and a particular SAN is unfavorable for optical signal transmission, another SAN with more favorable atmospheric conditions is selected. You can decide to use For example, the southwestern portion of the continental United States has relatively clear skies. In line with this, the placement of SANs in these clear locations within the country means that when the skies between SANs and satellites in other parts of the country are obstructed, transmissions over those SANs will occur. can provide an entry point for data that was supposed to be

Received/transmitted by satellites via one of several optical receivers/transmitters, in addition to directing satellites to communicate with those SANs that have a favorable atmospheric path to/from the satellite Signals can be directed to one of several antennas for transmission to selected user beam coverage areas. The flexibility in determining the sources of optical signals that can be received on the optical uplink, combined with the ability to select the particular antennas on which the signals received from the sources are to be transmitted, allows the system to: It is possible to mitigate the adverse effects of variable atmospheric conditions between the SAN and the satellite.

As disclosed herein, at least three different techniques can be used to convey information from the SAN, via satellites, to the user beam coverage areas where user terminals may reside. can. Three such techniques are described below. A very brief overview of each is provided followed by a more detailed disclosure of each architecture.

Briefly, the first technique uses a binary modulated optical signal on the uplink. Several SANs each receive information sent to user terminals that are within the user beam coverage area. The optical signal is modulated with digital information. In some embodiments, each SAN transmits such binary modulated optical signals to satellites. The digital information may represent information intended to be transmitted to user beam coverage areas in which user terminals may reside. The signal is detected within the satellite using a photodetector, such as a photodiode. In some embodiments, the resulting digital signal is then used to provide binary encoding, such as binary phase shift keying (BPSK) to modulate an intermediate frequency (IF) signal. The IF signal is then upconverted to the satellite RF downlink carrier frequency. Modulating an RF signal with BPSK is relatively straightforward and has small size, power, and thermal adaptations on satellites. However, using BPSK as the baseband modulation for the RF signal on the customer downlink 114 may not provide the maximum capacity of the system. That is, the maximum potential of the RF user downlink 114 is reduced from what would be possible if a denser modulation scheme such as 16 QAM was used on the RF user downlink 114 instead of BPSK.

A second technique also uses a binary modulation scheme to modulate the optical signal on the uplink. The modulated optical signal is detected by a photodiode. The resulting digital signal is coupled to a modem. Modems encode digital information onto the IF signal using a relatively bandwidth-efficient modulation scheme, such as quadrature amplitude modulation (QAM). QAM as used herein includes, for example, Quadrature Phase Shift Keying (QPSK), Offset QPSK, 8 Phase Shift Keying, 16 QAM, 32 QAM, Amplitude Phase Shift Keying (APSK), and related modulation formats. is used to refer to modulation formats that encode more than 2 bits per symbol. The use of denser QAM schemes results in more efficient use of the RF user link, but the use of such encoding on the RF user downlink 114 requires relatively complex digital/ Requires an intermediate frequency (IF) conversion block (eg, modem). Such complexity increases size, mass, cost, power consumption, and heat dissipation.

A third technique uses an RF modulated optical signal (as opposed to the binary modulated optical signal of the first two techniques). In this embodiment, rather than modulating an optical signal with digital information that is transmitted into the user beam coverage area, the RF signal is directly modulated (ie, intensity modulated) onto an optical carrier. The satellite then need only detect the RF modulated signal from the optical signal (i.e., detect the intensity envelope of the optical signal) and frequency upconvert the signal to the user downlink frequency, resulting in a composite The need for modems is removed from the satellite. The use of RF modulated optical signals reduces satellite complexity while increasing the overall capacity of the communication system by allowing for more dense modulation of the user link RF signals. Due to the bandwidth available in optical signals, many RF carriers can be multiplexed onto the optical carrier. However, an optical signal that is intensity modulated with an RF signal is susceptible to errors due to several factors, including fading of the optical signal.

Each of these three technologies suffers from the fact that there is an unreliable optical channel from the SAN to the satellite. Therefore, three system architectures are discussed to mitigate the problem of unreliable optical feeder link channels. Each configuration uses an additional SAN to compensate for the inherent unreliability of the optical link to the satellite. Signals can be sent from any SAN to any user beam coverage area. Using additional SANs ensures that the desired number of SANs with high quality optical links to satellites are available. In addition, flexibility in choosing routes through the satellite (i.e., what is referred to herein as "feederlink diversity") allows data to be routed over feederlinks from those SANs that have optical channels of the desired quality. It can be transmitted to satellites and to user spot beams on user links in a flexible manner.

Each of these three techniques will now be discussed in detail. Each of these technologies is discussed in the context of embodiments having a specific number of components (ie, SANs, lasers in each SAN, transponders in satellites, etc.). However, such specific embodiments are provided merely for clarity and ease of discussion. Additionally, a wide range of IF and/or RF frequencies, optical wavelengths, number of SANs, number of transponders on satellites, etc. are within the scope of disclosed embodiments. Accordingly, specific frequencies, wavelengths, antenna array elements, and similar parallel channels, components, devices, number of user beam coverage areas, etc. are not expressly limited by the claims appended hereto. Insofar it should not be viewed as a limitation as to the manner in which the disclosed system may be implemented.

FIG. 4 is a simplified schematic of the first of the above three techniques. A system 600 for implementing the first technique includes a plurality of SANs 602, a satellite 604 with at least one single-fed antenna 638, 640 per beam, and a user beam coverage area 1801 (see FIG. 19). ) and a plurality of user terminals 606 within. Alternatively, any antenna can be used, such as a direct radiating antenna, the antenna having multiple inputs, each of which can transmit in a user spot beam into the user beam coverage area. possible signals can be received. Antennas 638, 640 may be part of a direct-radiating array or reflector/antenna system. In some embodiments, system 600 has M SANs 602 . In exemplary system 600, and for each of the embodiments discussed throughout this disclosure, M=8. However, none of the systems disclosed herein are limited to this number. M=8 is merely a convenient example, in other embodiments M is 2, 4, 10, 12, 16, 20, 32, 40, or any other suitable value. be able to. In some embodiments, SAN 602 receives "outbound traffic" conveyed through the system from sources (such as core nodes not shown), which originate from information networks (e.g., the Internet). can receive Data communicated from core nodes to SAN 602 may be provided in any form that enables efficient communication of data to SAN 602, including in the form of a binary data stream. In some embodiments, the data is provided as a binary data stream modulated onto optical signals and transmitted over optical fibers to the SAN. Outbound traffic is received in streams identified in a particular user beam coverage area 1801 . In some embodiments, the data may also be associated with a particular user terminal or group of user terminals to which the data is sent. In some embodiments, data is associated with terminals based on the frequency and/or timing of signals carrying the data. Alternatively, a data header or other identifier may be provided with, included with, or within the data.

As received, the forward traffic is a binary data stream 601 . That is, in some embodiments the forward traffic is a binary representation, such as an intensity modulated or phase modulated optical signal. In alternate embodiments, the outbound traffic can be decoded into any other binary representation.

FIG. 5 shows the relationship between IF signal 903, optical channel 915, and optical bands 907, 909, 911, 913 used by the system in some embodiments. The selection of specific bandwidths, frequencies, number of channels, and wavelengths are merely examples provided to facilitate the disclosure of concepts. Alternate modulation schemes can be used, as well as other optical wavelengths, number of channels, and other RF and/or IF bandwidths and frequencies. The scheme shown is provided merely to illustrate one particular scheme that may be used. As shown, a plurality of 3.5 GHz wide binary modulated IF signals (eg, 64) 903 carry the binary data transmitted in one user spot beam. Examples of other bandwidths that can be used include 500 MHz, 900 MHz, 1.4 GHz, 1.5 GHz, 1.9 GHz, 2.4 GHz, or any other suitable bandwidth.

The binary (i.e., digital) content modulated onto each 3.5 GHz wide binary modulated IF signal 903 is represented by one of the 16 optical channels within one of the four optical bands 905. Used to perform intensity modulation. In some embodiments, the four bands 907, 909, 911, 913 of the optical spectrum are 1100 nm, 1300 nm, 1550 nm and 2100 nm. On the other hand, a band may be selected that lies anywhere within the useful light spectrum (ie, at least the minimally usable portion of the light spectrum without excessive attenuation during atmospheric transit). In general, optical bands are selected that have less attenuation than non-selected bands. That is, some light bands may have less attenuation than the rest of the light bands. In such embodiments, a subset of those optical bands is selected. Some of those selected bands may exhibit very similar attenuation.

In one embodiment, each optical channel is defined by the wavelength at the center of the channel, and each optical channel is spaced approximately 0.8 nm apart (ie, 100 GHz wide). Although the RF signal 903 being modulated onto the optical channel is only 3.5 GHz wide, the spacing allows the optical signal to be efficiently demultiplexed. In some embodiments, each SAN 602 wavelength division multiplexes several (eg, 64) such 3.5 GHz optical signals 903 (eg, 4×16) together onto an optical output signal. (WDM). Accordingly, 64 optical channels of digital content can be transmitted from one SAN 602 .

FIG. 6 shows an optical transmitter 607 used to optically modulate a binary data stream 601 onto an optical signal. According to an embodiment implementing the scheme shown in FIG. 5, optical transmitter 607 includes four optical band modules 608a-608d (two shown for simplicity) and optical combiner 609. . Each of the four optical band modules 608 includes 16 optical modulators 611 (two are shown for simplicity), for a total of 64 modulators 611 . Each of the 64 modulators 611 outputs an optical signal present in one of the 64 optical channels 915 (see FIG. 5). The channels are divided into four optical bands 907,909,911,913.

Modulator 611 determines optical channel 915 based on wavelength λ 1 of light source 654 generating the optical signal. MZM 652 intensity modulates the output of first light source 654 with an intensity proportional to the amplitude of binary data stream 601 . Binary data stream 601 is summed with a DC bias in adder 656 . Since the binary data stream 610 is a digital signal (ie, a signal with only two amplitudes), the resulting optical signal is a binary modulated optical signal. The modulated optical output from MZM modulator 652 is coupled to optical combiner 609 . In systems using modulation schemes such as the one illustrated in FIG. 5, each of the 16 light sources 654 residing within the same optical band module 608 emits an optical signal at one of 16 different wavelengths λ1. to output The 16 wavelengths correspond to the 16 optical channels 915 within the first optical band 907 . Similarly, light source 654 in optical modulator 611 in each of the other optical band modules 608 outputs an optical signal having wavelength λ 1 equal to the wavelength of the channels in the corresponding optical band 909 , 911 , 913 . Correspondingly, the 64 optical outputs 915 from the four optical band modules 608 a - 608 d each have a different wavelength, the 4 wavelengths defined by the wavelength λ 1 of the signals generated by the 64 light sources 654 . within 16 optical channels of one band. Optical combiner 609 outputs a wavelength division multiplexed (WDM) optical signal 660 that is a composite of each signal 915 .

SAN 602 transmits an optical signal 660 to satellite 604 via optical feeder uplink 108 (see FIG. 4). Optical signals emitted by optical transmitter 607 are received by lens 610 in satellite 604 . In some embodiments, lens 610 is part of a telescope within optical receiver 622 . In some embodiments, lens 610 is steerable (i.e., can be oriented to point at any one of several SANs 602 in the system, or any one within a subset). . The ability to point lens 610 at more than one of SANs 602 allows lens 610 to point at SANs 602 that have optical paths to satellites that are not currently suffering from signal fading. Lens 610 may be oriented using a mechanical two-axis positioning mechanism. Aiming the lens measures the received signal strength of a signal transmitted over an optical channel and uses this signal strength to establish a SAN that has optical links of sufficient quality (i.e., above a desired quality threshold). can be achieved by identifying when the lens is aimed at . Either ground commands or onboard processing may provide instructions to the lens positioning mechanism to precisely point the lens 610 at the desired SAN 602 .

Optical receiver 622 further includes an optical demultiplexer 650, such as a filter or prism. The optical receiver 622 has multiple outputs, each output corresponding to an optical wavelength. As shown in FIG. 4, optical receiver 622 has 64 outputs. However, as noted above, the selection of particular frequencies, numbers of optical bands, and wavelengths, and thus the number of outputs from optical receiver 622, are provided herein merely as examples and are not intended for systems such as system 600. It is not intended to limit the system to any particular number.

In some embodiments, each wavelength lies within one of four optical bands 907 , 909 , 911 , 913 . Each optical wavelength is centered in an optical channel. Optical channels within one band are spaced approximately 0.8 nm apart (ie, 100 GHz). Fabricating the optical channels throughout the interval makes it easier to provide an optical demultiplexer 650 that can demultiplex optical signals to provide each of the 64 optical channels on separate outputs. Become. In some embodiments, an additional lens 613 is provided to focus the output of optical demultiplexer 650 onto the input of a photodetector such as photodiode 612 . Photodiode 612 produces an electrical signal by sensing the intensity envelope of optical signal 660 provided at the optical input to the photodiode. In some embodiments where optical signal 660 is intensity modulated to one of two intensity levels, the first intensity level representing a logical "1" is the first amplitude level that also represents a logical "1". resulting in an electrical signal having A second intensity level representing a logical "0" results in an electrical signal having an amplitude representing a logical "0". Thus, the electrical signal is placed in a first state when the intensity of optical signal 660 is in a state representing a logical "1" and in a state in which the intensity of optical signal 660 represents a logical "0". time is placed in the second state. Correspondingly, the optical receiver has multiple digital outputs 615 . The electrical signal output from digital output 615 of photodiode 612 is coupled to modulator 614, such as a two-phase modulator. In some embodiments, such as the embodiment of FIG. 4, an LNA 617 is provided between photodiode 612 and two-phase modulator 614 . The output of bi-phase modulator 614 is a BPSK modulated IF signal (ie, an analog signal) having two phases. BPSK modulator 614 outputs a signal having a first phase representing a logical "1" in response to an electrical input signal of a first amplitude (ie, being in a first state). When the input to modulator 614 has an amplitude (i.e., second state) representing a logic "0", the phase of the output of BPSK modulator 614 is a second phase different from the first phase. is shifted to The output of modulator 614 is coupled to the input of switch matrix 616 .

In the simplified schematic diagram of FIG. 4, a second SAN 602 , a lens 610 , an optical receiver 622 and a plurality (ie, 64) of binary phase modulators 614 are coupled to a switch matrix 616 . Although only two SANs 602 are shown in FIG. 4, it should be understood that a satellite may receive optical signals from several (eg, eight) SANs 602 .

In some embodiments, the switch matrix 616 shown in FIG. 4 has multiple (eg, 64) inputs for each lens 610 . That is, if satellite 604 has eight lenses 610 , matrix switch 616 has 512 inputs, each coupled to one of modulators 614 . Switch matrix 616 allows signals at the outputs of switch matrix 616 to be selectively coupled to the inputs of switch matrix 616 . In some embodiments, any input can be chained to any output. On the other hand, in some embodiments, only one input can be tied to any one output. Alternatively, inputs and outputs are grouped such that inputs can only be connected to outputs within the same group. Limiting the number of outputs to which an input can be chained reduces the flexibility of the system, but reduces the complexity of switch matrix 616 .

Each output of switch matrix 616 is coupled to an upconverter 626 . Upconverter 626 upconverts the signal to the frequency of the user downlink carrier. For example, in some embodiments, the signal output from switch matrix 616 is a 3.5 GHz wide IF signal. A 3.5 GHz wide IF signal is upconverted to an RF carrier with a 20 GHz center frequency. The output of each upconverter 626 is coupled to a corresponding power amplifier 630 . The output of each amplifier 630 is coupled to one of multiple antenna inputs, such as one input of antennas 638, 640 (eg, antenna feeds not shown). Accordingly, each of the outputs of switch matrix 616 is effectively coupled to a corresponding one of the antenna inputs. In some embodiments, each input of each antenna 638, 640 transmits user spot beams to one user beam coverage area 1801 (see FIG. 19). A switch matrix 616 can select which input (ie, bi-phase modulator 614) is coupled to which output (ie, upconverter 626). Correspondingly, when (or before) the signal from one of the SANs 602 fades and the errors become unacceptable, the switch matrix 616 switches the upconverter 626 (i.e., the associated antenna feed section) can be coupled to a SAN 602 transmitting an optical signal that does not exhibit significant fading. In some embodiments, switch matrix 616 distributes content from a particular SAN to two or more user spot beams (i.e., antenna feeds) to distribute content fed to the antenna inputs. can be time division multiplexed.

That is, when each lens 610 is receiving a signal from the SAN 602 in the direction it is facing, each of the 64 outputs from the optical receiver 622 associated with that lens 610 will have a signal. become. In embodiments where each antenna input to antennas 638, 640 transmits a user spot beam to a particular user coverage area 1801, all user coverage areas 1801 will receive the signal (switch matrix 616 is , are mapped such that each input is concatenated into one output). A switch matrix 616 couples which analog outputs from the binary phase modulator 614 to respective antenna inputs (i.e., within each user spot beam) (e.g., each of the single-fed antennas 638, 640 per beam). to the other power supply). On the other hand, if the optical signal from a particular SAN 602 fades, the signal is still provided to all antenna inputs and no user coverage area 1801 loses coverage. One SAN 602 can provide signals to 65 or more user coverage areas 1801 by time division multiplexing signals from one SAN onto 65 or more antenna inputs. Although the total capacity of the system is reduced, the availability of the system to serve content to each user coverage area is enhanced. This is beneficial in systems with optical feeder links. In some embodiments, such time division multiplexing is performed for a short period of time while a lens 610 directed to a SAN 602 with a weaker optical link is redirected to another SAN with a stronger optical link. will be More generally, the matrix 616 can be used to time division multiplex the analog signal output from the optical receiver 622 into two or more user spot beams, and during the first period the analog The signal is coupled to a first antenna input (eg, feed) that transmits a user spot beam directed to a first user beam coverage area. During a second time period, the analog signal is coupled to a second antenna input (eg, feed) that transmits a user spot beam directed to a second user beam coverage area.

Once each lens 610 is receiving a sufficiently strong optical signal, the switch matrix 616 can again map each output to a unique output in a one-to-one correspondence from input to output. In some such embodiments, control of switch matrix 616 is provided by telemetry signals from a control station. In most embodiments, all 64 IF signals from the same SAN 602 will degrade together, so switch matrix 616 need only be able to select between K/64 outputs. where K is the number of user spot beams and 64 is the number of photodiodes 612 in one optical receiver 622 . As described above, the process of controlling the selection of paths through satellites to map SAN 602 to user spot beams is referred to herein as feeder link diversity. As discussed below, feeder link diversity can be provided in three different ways.

In some embodiments, satellite 604 has more antenna inputs than transponders (ie, paths from optical receivers to switches 634, 636). That is, a limited number of transponders, including power amplifiers (PAs) 630, upconverters 626, etc., can be used to transmit signals to a relatively greater number of user beam coverage areas. By sharing transponders between antenna inputs, the output from each photodiode 612 is time division multiplexed to provide multiple user beam coverage, which is greater than the number of transponders provided on satellite 604. Can provide information to the area. In this embodiment, RF switch 634 is used to direct the output of PA 630 to different inputs of one or both of antennas 638, 640 at different times. The times are adjusted so that the information present on the signal is intended to be transmitted to the user beam coverage area facing the input (ie, facing the feed). Accordingly, one transponder can be used to provide information to several user beam coverage areas in a time division multiplexed manner. By setting the switches 634, 636 to direct the signals to specific antennas 638, 640, the signals received by each of the lenses 610 can be directed to specific spot beams. This provides flexibility in dynamically allocating system capacity.

Switches 634, 636 direct the signal to the input of either antenna 638, 640 onboard the satellite. In some embodiments, outputs from switches 634, 636 may be directed to a subset of antennas. Each antenna 638, 640 is a single feed per beam antenna aimed at a specific user beam coverage area, thereby creating a spot beam. In an alternative embodiment, the PA 630 may be directly connected to the antenna input and the matrix switch 616 determines which signal detected by each particular photodiode 612 is transmitted to which user beam coverage area. to decide. Additionally, having switches 634, 636 can reduce the complexity of switch matrix 616, even in embodiments where there are equal numbers of satellite transponders and antenna inputs. That is, when switch matrix 616 and switches 634, 636 are used in combination, switch matrix 616 may not be able to couple each input to each output. Rather, matrix inputs, outputs, and antenna inputs can be grouped such that any input in a group can only be connected to any output in the same group as it. Switches 634, 636 can switch antenna inputs (eg, feeds) such that one group of outputs can be coupled to another group of antenna inputs.

Switch matrix 616 may operate in static or dynamic time division multiple access mode. In a static mode of operation, the configuration of paths through switch matrix 616 remains essentially fixed for relatively long periods of time. The configuration of switch matrix 616 is changed only to accommodate changes in the amount of transmitted traffic over relatively long periods of time, changes in the quality of a particular link over time, and the like. In contrast, in dynamic time division multiple access mode, switch matrix 616 is used to time division multiplex data between different forward downlink antenna inputs. Correspondingly, the switch matrix 616 selects which inputs are coupled to the outputs of the switch matrix 616 . This selection is based on whether the input signal is strong enough such that the number of errors in demodulating the signal at the user terminal 842, 844 is acceptable. In some such embodiments, one SAN 602 provides information for more than one user beam coverage area by time division multiplexing the analog outputs of optical receivers 622 to different antenna inputs. becomes possible. During the first time period, the one or more signals output from optical receiver 622 are each uniquely one of the first set of antenna inputs (i.e., the first of the user beam coverage areas). antenna input directed to a unique one of the set of 1). During the second period, one or more of those same signals can be coupled to different antenna inputs (ie, different user beam coverage areas). Such time-division multiplexing of the analog output 615 from the optical receiver 622 is useful if one of the lenses 610 of the optical receiver 622 is in a "weak" SAN 602 (i.e., a SAN with an optical link below the quality threshold). 602). In such an embodiment, a first data stream initially set to a weak SAN 602 is redirected by the core node to a "strong" SAN 602 (i.e., a SAN 602 with an optical link above the quality threshold). be able to. Strong SAN 602 time division multiplexes the information so that for a fraction of the time, strong SAN 602 is in the first set of user beam coverage areas intended for the first data stream. Send targeted information. During the second time period, strong SAN 602 transmits a second data stream directed to a second set of user beam coverage areas. In line with this, information that may have been blocked from reaching satellite 604 by a poor optical link between SAN 602 and satellite 604 for a period of time is sent to satellite 604 via strong SAN 602 . can be sent to During this time, lens 610 pointing at weak SAN 602 can be redirected to point at strong SAN 602 that has not yet transmitted to satellite 604 . As noted above, this process of redirecting information from weak SANs to strong SANs is an aspect of feeder link diversity.

By determining when the feeder uplink signal is exhibiting unacceptable fading, data can be moved away from the SAN 602 using the faulty feeder uplink to a feeder with acceptable signal levels. It can be sent to SAN 602 with an uplink signal. Through the process of feeder link diversity, signals transmitted over the selected SAN 602 can then be routed through the switch matrix 616 to the spot beams intended for the data destination.

System 600 has the advantage of being relatively simple to implement inside satellite 604 . Conversion of binary modulated optical data to a BPSK modulated IF signal using photodiode 612 and binary phase modulator 614 is relatively straightforward. Such a two-phase modulator is relatively easy and inexpensive to build, requires relatively little power, and can be relatively small and lightweight. However, using BPSK modulation on the RF user downlink 114 does not make the best use of the finite RF spectrum. That is, achieving a higher capacity RF user downlink 114 by using a denser modulation scheme such as 16QAM instead of BPSK on the RF user downlink 114 (see FIG. 1). can be done.

For example, in an alternative embodiment of system 600 implementing the second of the three techniques above, analog signal 618 to be transmitted on the user downlink is modulated with a denser modulation scheme. Since it produces a complex modulation on the analog signal 618, the modulator is a highly complex modulator that takes a digital data stream and converts the data stream into one or more complex modulated signals. There must be. Composite modulated signal 618 can be, for example, a higher order modulation such as 64-QAM, 8psk, QPSK. Alternatively, any other modulation scheme can be used that allows the symbols to be modulated onto the IF carrier, where the symbols represent more than two logical states. That is, the binary intensity modulation of the optical signal results in the output 615 of the optical receiver 622 providing an electronic signal with binary modulation representing the original content. To modulate analog signal 618 with a more complex modulation scheme, such as 16QAM, modulator 614 is a QAM modulator and therefore performs QAM modulation of the IF signal based on the digital content output from photodiode 612. conduct.

Accordingly, in some embodiments, the biphasic modulator 614 of system 600 is replaced with a QAM modulator 614 (ie, a modulator in which each symbol represents 3 or more bits). Correspondingly, rather than restricting the modulation of IF signal 618 to a binary modulation scheme (i.e., two logical states) such as BPSK, modulator 614 allows IF signal 618 to be modulated into a more dense modulation scheme. (ie, a scheme in which a symbol can represent more than two values, such as QAM). A more complex QAM modulator provides more efficient modulation of the IF signal 618 (QAM vs. BPSK), but is more complex, requires more power, and weighs more than a two-phase modulator. and expensive.

FIG. 7 is an illustration of the return path of system 600 . User terminal 606 transmits a binary modulated signal to satellite 604 . A switch 402 coupled to each element of the antenna (e.g., single-beam antennas 404, 406 per feed) controls the satellite transponder, including a low noise amplifier (LNA) 408, a frequency converter 409, and a digital decoder 410. to choose from. Frequency converter 409 downconverts the received signal from the user uplink frequency to IF. Decoder 410 decodes the binary modulation on the received IF signal. Accordingly, the output of each decoder 410 is a digital signal. Digital decoder 410 is coupled to the input to switch matrix 416 . Switch matrix 416 modulates the signals received via each of the user spot beams onto different optical links depending on whether there is significant fading on the optical downlink to each SAN 602. (ie, sent to different SANs 602). The output of switch matrix 416 is coupled to the input to optical transmitter 607 . Each optical transmitter 607 is essentially the same as the optical transmitter 607 described above and shown in FIG. In some embodiments, where the optical spectrum is used in essentially the same manner as it is used on the forward feeder link (see FIG. 5), each of the four optical band modules 608 is a matrix It receives 16 outputs from switch 416 for a total of 64 inputs to optical transmitter 607 . In some embodiments where a satellite can receive optical signals from eight SANs 602, there are eight such optical transmitters 607 that can receive a total of 512 outputs from switch matrix 416. do. Each optical transmitter 607 outputs an optical signal 660 . Optical signal 660 is received by lens 412 internal to optical receiver 414 in SAN 602 . Optical receiver 414 and lens 412 are essentially the same as optical receiver 622 and lens 610 internal to satellite 604, as described above with reference to FIG. Accordingly, the output of optical receiver 414 is a binary data stream. The output of the optical receiver is transmitted to an information network, such as the network that provided forward traffic to SAN 602 .

In an alternative embodiment, which is the return link of system 600, the modulation used on the return uplink from user terminal 606 to satellite 604 is a more efficient modulation scheme than binary modulation. Along with this, binary modulation 410 is a more complex modulator 410 . The binary data output from demodulator 410 is the result of decoding the modulation symbols modulated onto the IF signal by user terminal 606 . For example, if 16QAM is used on the user uplink, the signal output from the demodulator is a digital stream of values represented by 16QAM symbols. The binary signal output from converter 502 is coupled to the input to switch matrix 416 . Both the binary demodulator and the composite demodulator 410 output digital data streams that are used to perform binary modulation of the optical signal transmitted by the optical transmitter 607 on the feeder downlink.

FIG. 8 is a simplified schematic diagram of a system 800 for implementing the third technique. In some embodiments of system 800 , SAN 802 receives forward traffic as “baseband” signal 809 coupled to the baseband input to IF converter 1605 . In some embodiments, seven 500 MHz wide baseband subchannels 809 are combined into a 3.5 GHz wide IF signal 811 . Each of the 3.5 GHz wide signals 811 is transmitted to one user coverage area 1801 . FIG. 9 illustrates the relationship between baseband subchannels 809, IF signals 811, and optical signals within system 800. FIG.
Examples of other bandwidths that can be used include 500 MHz (e.g., a single 500 MHz subchannel), 900 MHz, 1.4 GHz, 1.5 GHz, 1.9 GHz, 2.4 GHz, or any other suitable bandwidth.

FIG. 10 is a simplified illustration of a SAN 802, such as SAN 802 shown in FIG. In some embodiments, there are 64 baseband-to-IF converters 1605, which are shown organized into four IF combiners 1602, each with 16 conversions. 1605. The grouping of baseband to IF converters 1605 within IF converter 1602 is not shown in FIG. 8 for simplicity of illustration. Each of the 64 baseband-to-IF converters 1605 has S inputs, where S is the number of subchannels 809 . In some embodiments where subchannel 809 has a bandwidth of 500 MHz and signal 811 has a bandwidth of 3.5 GHz, S is equal to seven. Each input couples one of the subchannels 809 to a corresponding frequency converter 1606 . Frequency translator 1606 provides a frequency offset such that a subset of subchannels 809 (eg, S=7 in FIG. 10) can be added in adder 1608 . Accordingly, in some embodiments, such as that illustrated in FIG. 10, SAN 802 handles 64 channels, each 3.5 GHz wide. In some embodiments, the 3.5 GHz wide signal can be centered at DC (ie, using zero-IF modulation). Alternatively, signal 811 can be centered on a particular RF frequency. In one particular embodiment, RF carrier 811 is centered on the RF downlink frequency (in which case the satellite would not need upconverter 626, as further described below). The output 811 from each summing circuit 1608 is an IF signal 811 that is coupled to one of the 64 optical modulators 611 . The 64 optical modulators 611 are grouped into 4 optical band modules 608 . Each light modulator 611 operates in essentially the same manner as the light modulators 611 shown in FIG. 6 and described above. However, since the input 811 to each optical modulator 608 is an analog signal, the optical signal output from each optical modulator 611 is an intensity-modulated optical signal having an amplitude envelope according to the amplitude of the IF signal 811. be.

Optical combiner 609 combines the outputs from each of 64 optical modulators 611 to produce wavelength division multiplexed (WDM) combined optical signal 1624 . The number of baseband to IF converters 1605 and the number of optical modulators 611 in the optical band module 608 can vary. As shown in FIG. 9, the four optical modulators 611 are designed to output optical signals with wavelengths of 1100 nm, 1300 nm, 1550 nm and 2100 nm centered. be able to.

In system 800 , optical transmitter 607 (similar to optical transmitter 607 in FIG. 4) emits RF modulated composite optical signal 1624 . RF modulated composite optical signal 1624 is received by lens 610 inside satellite 804 (see FIG. 8). Lens 610 can be aimed at any of a plurality of SANs 802 that can transmit optical signals to satellites 804 . The output of lens 610 is coupled to the input of a photodetector, such as photodiode 612 (eg, PIN diode). Photodiode 612 senses the envelope (ie, intensity profile) of the optical signal and converts the envelope of the optical signal into an electrical signal. Since the optical signal is intensity modulated with IF signal 811, the resulting electrical signal output from photodiode 612 is essentially the same as IF signal 811 modulated onto composite optical signal 1624 by SAN 802. is. Photodiode 612 is coupled to amplifier 808 . The signal output from amplifier 808 is then coupled to the input of matrix switch 616 . Matrix switch 616 functions similarly to matrix switch 616 discussed above with respect to FIG. Correspondingly, the switch matrix 616 selects which inputs are coupled to the outputs of the switch matrix 616 . The output of matrix switch 616 is processed in the same manner as in system 600 described above in embodiments where signal 811 is at zero IF. In embodiments where the signal 811 output in the SAN from baseband to IF module 607 is located at the frequency that is transmitted directly from satellite 804, the processing is similar, except that upconverter 626 is not required. become.

FIG. 11 is an explanatory diagram of the return link of system 800. As shown in FIG. The return link of system 800 is essentially the same as shown in FIG. However, rather than user terminal 606 transmitting a signal with binary modulation, user terminal 606 transmits a signal with a more efficient modulation (eg, 16QAM instead of QPSK). Correspondingly, output digital decoder 410 is not required. Downconverter 850 downconverts the RF frequency being used on the customer uplink to the appropriate IF frequency. In some embodiments, the IF frequency signal is a 3.5 GHz wide zero IF signal. The output of each downconverter 850 is coupled to the input of switch matrix 416 . As such, the input of MZM modulator 652 (see FIG. 6) receives analog signals from switch matrix 416 . Accordingly, the output of each optical modulator 611 is an intensity modulated optical signal whose intensity envelope tracks the signal output from downconverter 850 . In some embodiments, optical modulator 611 modulates the RF user uplink frequency directly onto the optical signal. Correspondingly, frequency converter 850 is not required. In embodiments in which downconverter 850 reduces the user uplink frequency to a zero-IF signal, combined optical signal 660 is processed similarly as discussed with respect to FIG. In embodiments where the optical signal is modulated at the user uplink frequency, a downconverter may be included within modem 418 or prior to coupling the signal from optical receiver 414 to modem 418 .

We have discussed three different techniques for modulating the signal on the feeder link, each of which uses a first system architecture, which converts the received carrier into a user spot beam It has satellites that use a matrix switch 616 to allow flexible assignment to. The second and third system architectures will now be discussed. A second system architecture includes satellites with onboard beamforming. A third system architecture uses terrestrial beamforming.

FIG. 12 is a simplified schematic diagram of a system 1000 using the technique shown in FIG. 4 (i.e., modulating an optical feeder uplink with binary modulation and using that binary content to link). However, system 1000 uses a second system architecture in which satellites 1004 are capable of on-board beamforming. System 1000 operates similarly to system 600 described above. However, the IF output from each bi-phase modulator 614 is coupled to weighting/combiner module 1006 rather than switch matrix 616 .

FIG. 13 is a simplified block diagram of weighting/combiner module 1006 in which K forward beam signals 1002 are received by beamformer input module 1052 within weighting/combiner module 1006 . K signals 1002 are sent to split N path module 1054 via input module 1052 . An N-path splitting module 1054 splits each of the K signals 1002 into N copies of each forward beam signal, where N is the antenna array used to form the K user spot beams. is the number of elements in

In the example system described above with respect to FIG. 4, there are eight active SANs, each transmitting optical signals containing 64 optical channels. Each of the 64 optical channels carries a 3.5 GHz IF signal (ie, forward beam signal). Therefore, there are 512 forward beam signals (ie, 8 SANs x 64 IF signals). Correspondingly, K=512. In some embodiments, the satellite has an antenna array 1008 with 512 array elements. Accordingly, N=512.

Each output from N-path splitting module 1054 is coupled to a corresponding input of one of 512 weighting and summing modules 1056 . Each of the 512 weighting and summing modules 1056 includes 512 weighting circuits 1058 . Each of the 512 weighting circuits 1058 applies a weight to (ie, amplifies and phase shifts) a corresponding one of the 512 signals output from the N-path splitting module 1054 . The weighted outputs from weighting circuit 1058 are summed by summer 1060 to form 512 beam element signals 1062 . Each of the 512 beam element signals 1062 is output via a beamformer output module 1064 . 12, each of the 512 beam element signals 1062 output from the weighting/combiner module 1006 is coupled to a corresponding one of the 512 upconverters 626. Upconverter 626 is coupled to PA 630 . Each output of PA 630 is coupled to a corresponding one of the 512 antenna elements of antenna array 1008 . Antenna arrays include direct-radiating arrays (each antenna element emits directly in a desired direction), array-fed reflectors (each antenna element illuminates a reflector shared by all antenna elements), or any of any other suitable antenna configuration. The combination of antenna array 1008 and weighted combiner module 1006 is also referred to as a phased array antenna.

When the relative weights of the signals are applied to the elements at their respective locations within the phased array antenna 1008, the multiple weighted signals are superimposed on top of each other and thus coherently combined to form a user beam. It will be.

Correspondingly, by applying the desired weightings to the plurality of signals 1002 to produce the beam element signals 1062 output from the weighting/combiner module 1006, the Signal 1002 can be directed to one of multiple user beam coverage areas. Satellite 1004 can use weighting/combiner modules 1006 and array antennas 1008 to direct any received signal to any user beam coverage area, thus avoiding a particular feeder exhibiting unacceptable fading. Information that was to be sent via the uplink can be sent to one of the other SANs. Accordingly, information is transmitted to satellites 1004 via SAN 602 that does not exhibit unacceptable fading, as described above in connection with matrix switch 616, to provide feedlink diversity. can do. Similar time division multiplexing can be performed to transmit the signal received by one of the lenses 610 as described above in several user spot beams.

Using satellites 1004 with onboard beamforming provides flexibility to allow feeder link diversity for signals received from multiple SANs 602 . The use of on-board beamforming obviates the switch matrix 616 shown in FIG. A similar architecture can be used on the return path (ie, user uplink and feeder downlink). That is, user ground terminal 606 transmits RF signals to satellite 1004 over the user uplink. Receiving elements in antenna array 1008 receive the RF signals. A weight/combiner module 1006 weights the received signals received by respective receive elements of antenna 1008 to form receive beams. The output from weighting/combiner module 1006 is downconverted from RF to IF.

In some embodiments, upconverter 626 is placed at the input of weighting/combiner module 1006 rather than at the output. Therefore, RF signals (eg, 20 GHz signals) are weighted and summed. The beam element signals are then transmitted via each of the antenna array elements.

In some embodiments, the satellite has several weighting/combiner modules (not shown for simplicity). Inputs to each weighting/combiner module are coupled to one or more optical receivers 622 . In some embodiments, all outputs from one optical receiver 622 are coupled to the same weighting/combiner module. Each weight/combiner module produces N outputs. The N outputs from each weighting/combiner module are coupled one-to-one to the elements of one N-element antenna array (only one is shown for simplicity). In line with this, there is a one-to-one relationship between the antenna array 1008 and the weighting/combiner modules 1006 .

In some embodiments, the second architecture (ie, on-board beamforming) shown in FIG. 12 is used with QAM modulator 614 similar to system 600 . However, satellite 1104 has onboard beamforming.

FIG. 14 is a simplified schematic diagram of a system 1200 using the techniques discussed with respect to FIG. 8 in which an optical signal is RF modulated in SAN 802. However, the satellite architecture is similar to that of Figures 12 and 11 with satellite 1204 having on-board beamforming capability. SAN 802, lens 810, photodetector (such as photodiode 812), amplifier 613, and upconverter 626 are all similar to those described with respect to FIG. The weighting/combiner module 1006 and array antenna 1008, on the other hand, are similar to those described with respect to FIGS. Similar to the architecture described in FIG. 12, weighting/combiner 1006 and array antenna 1008 allow satellite 1004 to combine the content of signals received from one or more of SANs 802 into any of the user beam coverage areas. , thereby providing feeder link diversity. Therefore, if one or more of the feeder uplinks from SAN 802 to the satellite has unacceptable fading, content that was to be sent on that feeder uplink will instead be sent on other feeder uplinks. SAN 802 using a feeder uplink that does not exhibit unacceptable fading.

FIG. 15 is an illustration of a forward link of a satellite communication system 1400 using a third system architecture (ie, terrestrial beamforming), including an optical forward uplink 1402 and a radio frequency forward downlink 1404 . In some embodiments, system 1400 compares for communicating with user terminals 806 located within 512 user beam coverage areas 1801 (see FIG. 19 discussed in detail below). It includes a forward link terrestrial beamformer 1406, satellites 1408, and a relatively large number (M) of SANs 1410 so as to create a highly reliable system of relatively high capacity. Throughout the discussion of system 1400, the example shows SAN 1410 with M=8. However, M=8 is merely a convenient example and is not intended to limit a disclosed system such as system 1400 to any particular number of SANs 1410 . Also, in the embodiment of system 1400, 64 optical channels are shown. Additionally, the antenna array is shown as having 512 elements. As noted above, specific frequencies, wavelengths, antenna array elements, and similar parallel channels, components, devices, numbers of user beam coverage areas, etc. are expressly defined by the claims appended hereto. should not be viewed as a limitation as to the manner in which the disclosed system may be implemented unless limited to

Outbound traffic conveyed through system 1400 (i.e., outbound beam input signal 1407) is initially beamformed from a source, such as the Internet, through distribution equipment, such as a core node or similar entity (not shown). provided to device 1406 . In addition to performing other functions, the distribution equipment manages the allocation of frequencies and/or time slots for transmission to individual user terminals and groups data for transmission destined for specific beams. good too. Input signal 1407 (or some portion of the information carried by forward beam input signal 1407) to beamformer 1406 is a data stream (or modulated data stream) directed to each of the 512 user beams. ) can be expressed. In one embodiment, each of the 512 forward beam input signals 1407 is a 3.5 GHz wide IF signal. In some embodiments, forward beam input signal 1407 is a composite 3.5 GHz wide carrier coupled to the input of beamformer 1406 .

Each forward beam input signal 1407 is “directed” by beamformer 1406 into user beam coverage area 1801 . A beamformer 1406 applies beam weights (as further described below with respect to FIG. 16) to the 512 forward beam input signals 1407 to form a set of N beam element signals 1409. directs the forward beam input signal 1407 to a particular user beam coverage area 1801 . Generally, N is greater than or equal to K. In some embodiments, N=512 and K=512. The 512 beam element signals 1409 are amplified and frequency converted to form RF beam element signals 1411 . Each is transmitted from an element of an N-element (ie, 512-element) antenna array 1416 . RF beam element signals 1411 overlap each other within user beam coverage area 1801 . The superposition of the transmitted RF beam element signals 1411 forms a user beam within the user beam coverage area 1801 .

In some embodiments, the 512 beam element signals 1409 are split among several SANs 1410 . Correspondingly, a subset (eg, 512/8) of beam element signals 1409 is coupled to each SAN 1410, where 8 is the number of SANs 1410. FIG. Thus, the combination of 8 SANs 1410 will transmit 512 beam element signals 1409 from beamformer 1406 to satellite 1408 . In some embodiments, beamformer 1406 is co-located with one of SANs 1410 . Alternatively, beamformer 1406 is located elsewhere. Further, in some embodiments, beamformers 1406 may be distributed among several locations. In one such embodiment, portions of beamformers 1406 are co-located with respective SANs 1410 . Each such portion of beamformer 1406 receives all of the forward traffic 1407, but 64 of them (i.e., 512/512/1410) transmitted to SAN 1410 co-located with that portion of beamformer 1406. 8) Apply beam weights to only one signal 1409; In some embodiments, several beamformers are provided (not shown for simplicity). Each beamformer produces N outputs (ie, beam element signals). The N beam element signals will be coupled one-to-one to the elements of one N-element antenna array (only one is shown for simplicity) on satellite 1408 . In line with this, there is a one-to-one relationship between antenna array 1416 and beamformer 1406 . All of the beam elements from one beamformer 1406 are transmitted to the satellite 1408 via one SAN 1410. In some embodiments, there is no need to coordinate the timing of transmissions from another SAN 1410. . Alternatively, in embodiments in which beam elements output from the same beamformer 1406 are transmitted to satellites 1408 over different SANs, the timing of the beam element signals uses timing control as discussed further below. are taken into account.

The phase relationship between each of the RF beam element signals 1411 transmitted from each of the N elements of the antenna array 1416, and the relative amplitude of each, allows the beam element signals to properly overlap to provide the desired user beam coverage area. It determines whether a beam is formed in 1801 or not. In some embodiments where there are eight SANs 1410 (ie, M=8), each SAN 1410 receives 64 beam element signals 1409 .

To maintain the phase and amplitude relationship of the 512 RF beam element signals 1411 to each other, the beamformer 1406 sends eight timing pilot signals 1413 in addition to the N beam element signals 1409 to each SAN. 1410 outputs one by one. Each timing pilot signal 1413 is aligned with other timing pilot signals upon transmission from the beamformer 1406 to each SAN 1410 . Additionally, the amplitude of each timing pilot signal 1413 is equal.

FIG. 16 is a detailed illustration of forward beamformer 1406 . Forward beamformer 1406 receives 512 forward beam signals 1407 representing forward traffic transmitted through system 1400 . Signal 1407 is received by matrix multiplier 1501 . Matrix multiplier 1501 includes beamformer input module 1502 , 512 path splitting module 1504 , and 512 weighting and summing modules 1506 . Other arrangements, implementations or configurations of matrix multipliers can be used. Each of the 512 forward beam signals 1407 is intended to be received within a corresponding one of the 512 user beam coverage areas 1801 . Correspondingly, there is a one-to-one relationship between the 512 user beam coverage areas 1801 and the 512 forward beam signals 1407 . In some embodiments, the distribution equipment (e.g., core node) that provides forward traffic to the beamformer 1406 determines that the information sent to a particular user beam coverage area 1801 corresponds to that user beam coverage area 1801. is included within forward beam input signal 1407.

The 512-path splitting module 1504 splits each of the 512 forward beam signals 1407 into 512 identical signals, resulting in 512×512 (ie, N×K) signals from the 512-path splitting module 1504 . output. If N equals 512 and K equals 512, then splitting module 1504 outputs 512×512=524,288 signals. The 512 unique signals output from splitting module 1504 are coupled to 512 weighting and summing modules 1506 . The signals coupled to each of the weighting and summing modules 1506 are weighted (ie, phase shifted and amplitude adjusted) according to beam weights calculated by the forward beam weight generator 1508 . Each of the 512 weighted signals corresponding to the same array element N are summed in one of 512 adders 1512 .

Timing module 1514 is provided because each group of 64 outputs from adder 1512 is to be coupled to and transmitted by a different one of eight SANs 1410. . The timing module 1514 ensures that each group of 64 IF beam element signals 1409 arrives at the user beam coverage area 1801 at the proper time so that the superposition of the signals 1409 is properly aligned with the user beam. Adjust the timing at which the beam element signals 1409 are sent from the beamformer to ensure good formation. Alternatively, forward beam weights can be generated to account for differences in path lengths and characteristics from each SAN 1410 to satellite 1408 . Correspondingly, signal 2122 would be coupled to forward beam weight generator 1508 . In some embodiments, timing module 1514 generates timing pilot signals 1413 that are transmitted from forward beamformer 1406 to respective SANs 1410 . In some embodiments, one timing pilot signal 1413 is generated and divided into eight copies of equal amplitude and one copy is sent to each SAN 1410 . Alternatively, the amplitudes of the copies may be a predetermined ratio. As long as the ratio between the timing pilot signals 1413 is known, the RF beam element signals 1411 can be equalized to ensure that they overlap each other to form the desired user spot beam. In some embodiments where corrections to alignment are made in timing module 1514 within beamformer 1406 , so that forward beamformer 1406 can determine corrections to alignment of signals to respective SANs 1410 . , each SAN 1410 returns a signal 2122 calculated from the SAN timing correction signal 1419 to the timing control input to the beamformer. In some embodiments, SAN timing correction signal 1419 is then used by timing module 1514 to adjust the timing of beam element signals 1409 . In another embodiment, SAN timing correction signal 1419 is used to adjust the beam weights to account for differences in paths from beamformer 1406 through each of SANs 1410 to satellite 1408 for forward beams. Used by weight generator 1508 . As noted above, corrections to alignment can alternatively be made at each SAN 1410 .

After the beam element signals 1409 have been appropriately weighted and any necessary timing adjustments made, each of the 512 signals 1409 is coupled to one of the SANs 1410 . That is, each of the eight SANs 1410 receives 64 beam element signals 1409 (ie, 512/8) from the forward beamformer 1406 . Optical transmitters 1401 in each SAN 1410 receive, multiplex, and modulate their 64 beam element signals 1409 onto an optical carrier.

FIG. 17 is an illustration of optical transmitter 1401 used in some embodiments of system 1400 . Optical transmitter 1401 is similar to optical transmitter 607 discussed above with respect to FIG. However, input signal 1409 is different because it has been beamweighted by beamformer 1406 . In addition, the timing pilot signal 1413 provided by the beamformer 1406 is coupled to the optical modulator 611 for other wavelengths within the same optical band module 1403 as determined by the wavelength of the light source 654 within that optical modulator 608 . is modulated onto the optical carrier within the same band as that of the optical modulator 611 of . In some embodiments, each optical band module 1403 is identical. However, modulating the timing pilot signal 1413 need only be done in one such optical band module 1403 . Alternatively, only one optical band module 1403 is configured to modulate the timing pilot signal 1413, as shown in FIG. Other light band modules 608 may be similar to the light band modules 608 described above and shown in FIG. In either embodiment, eight SANs 1410 each receive 64 beam element signals 1409 and distribute them over 16 optical channels in four different optical bands as shown in FIG. There are four optical band modules in optical transmitters 1401 in each SAN 1410 in the system.

Timing pilot signal 1413 follows the same path as IF beam element signal 1409 to the satellite. Thus, by comparing the arrival times of the timing pilot signals transmitted from each SAN 1410 at satellite 1408, the difference in the arrival times of the IF beam element signals can be determined and the correction signals generated, respectively SAN 1410 of . Similar to optical transmitter 607 , optical channels 915 output by respective optical modulators 611 shown in FIG. 17 are combined in optical combiner 609 . Combined optical signal 1624 is emitted from optical lens 2002 within optical transmitter 1401 . Optical lens 2002 operates as an optical signal transmitter capable of transmitting optical signals to satellite 1408 .

Composite optical signals 1624 from each of SANs 1410, including 64 beam element signals 1409 and timing pilot signals 1413, are transmitted over optical forward uplink 1402 to satellite 1408 to the eight optical receivers in satellite 1408. 1412. Each of eight optical receivers 1412 in satellite 1408 demultiplexes 64 optical channels 915 from composite optical signal 1624 .

FIG. 18 shows the components of satellite 1408 (see FIG. 15) in more detail. Satellite 1408 receives and transmits the forward link as described above with reference to FIG. 15, according to some embodiments of systems using terrestrial beamforming. Components of the forward link of satellite 1408 include eight optical receivers 1412 , eight amplifier/converter modules 1414 and a 512 element antenna array 1416 . In some embodiments of system 1400, there are eight SANs (ie, M=8), similar to the embodiments shown in FIGS. 9, 13, and 16, the received composite signal 1624 includes 64 optical channels divided into 4 bands of 16 each, each carrying a 3.5 GHz wide IF channel. In addition, there are K=512 user beam coverage areas 1801 and N=512 elements in the antenna array. As noted elsewhere in this discussion, these numbers are provided merely as an example and to facilitate discussion.

Each optical receiver 1412 is associated with a corresponding amplifier/converter module 1414 . Optical receivers 1412 each include a plurality of photodetectors, such as lens module 1701 and photodiode 1703 . Lens module 1701 includes lens 1702 (which in some embodiments may be similar to lens 610 described above with respect to FIG. 4), optical demultiplexer 1704, a plurality of optical demultiplexers 1706, and a plurality of optical demultiplexers 1706. output lens 1708 .

In operation, a combined optical signal 1624 is received from each of eight SANs 1410 . Lenses 1702 are provided to receive respective combined light signals 1624 . In some embodiments, lens 1702 can be focused (in some embodiments, mechanically aimed) at SAN 1410 from which combined optical signal 1624 received by lens 1702 originates. Lens 1702 can later be refocused to face another SAN 1410 . Satellite 1408 was selected from among the larger number of 8+X SANs 1410 because lens 1702 can be focused to receive composite optical signal 1624 from one of several SANs 1410. Signals can be received from eight SANs 1410 . In some embodiments, X=24. Thus, 32 different SANs 1410 can receive information intended to be conveyed to the user beam coverage area 1801 in the system. However, only 8 of the 32 SANs 1410 have information transmitted and are selected to be received by satellites 1408 .

The signal path of one of composite optical signals 1624 through the forward link of satellite 1408 is now described in detail. It should be appreciated that each of the eight signal paths taken by the eight received combined optical signals 1624 through the forward link of satellite 1408 function exactly the same. Composite optical signal 1624 received by lens 1702 is directed to optical demultiplexer 1704 . In a system using the modulation scheme illustrated in FIG. 9, optical demultiplexer 1702 divides combined optical signal 1624 into four bands 907, 909, 911, 913 (see FIG. 9). That is, optical demultiplexer 1704 splits combined optical signal 1624 into four optical wavelengths onto which beam element signals 1407 were modulated by SAN 1410 that transmitted combined optical signal 1624 . Each optical output from optical demultiplexer 1704 is coupled to a corresponding optical demultiplexer 1706 . Each of the four optical demultiplexers 1706 outputs 512/(4×8) optical signals for a total of 4×(512/(4×8)=512/8=64 optical signals. Each of the 16 optical signals output from the four optical demultiplexers 1706 is directed to an output lens 1708. Each of the output lenses 1708 focuses the corresponding optical signal onto a photodiode 1703 or the like. Each photodiode 1703 senses the amplitude envelope of the optical signal at its input and outputs an RF transmit beam element signal 1418 corresponding to the sensed amplitude envelope. Accordingly, RF transmit beam element signals 1418 output from optical receiver 1412 are essentially beam element signals 1409 modulated onto optical signals by SAN 1410 .

The RF output signal is then coupled to amplifier/converter module 1414 . Amplifier/converter module 1414 includes 512/8 signal paths. In some embodiments, each signal path includes a low noise amplifier (LNA) 1710, a frequency converter 1712, and a PA 1714. In other embodiments, the signal path includes only frequency converter 1712 and PA 1714 . In yet another embodiment, the signal path includes only PA 1714 (frequency converter 1712 can be omitted if the powering signal generated by the SAN is already at the desired forward downlink frequency). A frequency converter 1712 frequency converts the RF transmit beam element signal 1418 to the forward downlink carrier frequency. In some embodiments, the output of each upconverter 1712 is an RF carrier with a center frequency of 20 GHz. Each of the 512 outputs from the 8 amplifier/converter modules 1414 is coupled to a corresponding one of the 512 elements of the 512 element antenna array 1416 . Accordingly, antenna array 1416 transmits 512 forward downlink beam element signals 1718 .

FIG. 19 is an illustration of a user beam coverage area 1801 formed over the continental United States, according to some embodiments. In other embodiments, the user beam coverage areas may be located at different locations and with different spacings and patterns. In some embodiments, such as the embodiments shown in FIGS. 4, 8, and 12, each feed of the antenna is focused to direct a user spot beam into one user beam coverage area. are combined. In other embodiments, such as those shown in FIGS. 10, 11, 12, 14, and 14A, 512 forward downlink beam element signals 1718 are directed to user beam coverage area 1801. stacked on top of each other to form a single user beam. As shown in FIG. 19, the user beam coverage areas are distributed over a substantially larger satellite service area than the user beam coverage area 1801 . A 512-element antenna array 1416 transmits RF beam element signals 1411 to each of 512 user beam coverage areas 1801 via forward downlink 1404 . A user terminal 806 within each user beam coverage area 1801 can access that particular user beam coverage area by superposition of RF beam element signals 1411 transmitted from each of the 512 elements of the 512 element antenna array 1416 . A user beam directed at 1801 is received.

In addition to the IF beam element signals 1418 output from each optical receiver 1412 , each optical receiver 1412 demultiplexes the satellite timing signal 1415 from the composite optical signal 1624 . A satellite timing signal 1415 is output from each receiver 1412 and coupled to a corresponding amplifier/converter module 1414 . LNA 1710 within amplifier/converter module 1414 amplifies satellite timing signal 1415 . Output 1416 of LNA 1710 is coupled to satellite timing module 1417 . In some embodiments, satellite timing module 1417 compares satellite timing signals 1415 received by each optical receiver 1412 to determine if they are aligned. Satellite timing module 1417 outputs eight SAN timing correction signals 1419 that are returned one to each of the eight SANs 1410 . In some embodiments, each SAN timing correction signal 1419 is coupled to an input to a return amplifier/converter module 1904 (see FIG. 24). Each SAN timing correction signal 1419 is amplified, frequency translated to the forward downlink frequency, and sent out of eight optical transmitters 1401 in satellite 1408 similar to the optical transmitters 1401 provided in SAN 1410 . is connected to the input to one of the In some embodiments, one of the eight is a reference for the other seven. Accordingly, no corrections are made to the timing of signals transmitted from SAN 1410 that transmitted the reference satellite timing signals. Therefore, no SAN timing correction signal 1419 is sent to that SAN 1410 . SAN timing correction signals 1419 are modulated onto respective composite optical signals transmitted by satellites 1408 to respective SANs 1410 .

Each SAN timing correction signal 1419 provides timing alignment information indicating how offset the timing pilot signal 1413 is with respect to other timing pilot signals (eg, reference satellite timing signal 1415). In some embodiments, the timing information is sent via SAN 1410 to timing module 1514 in beamformer 1406 (see FIG. 16). Timing module 1514 adjusts the beam element alignments before sending them to respective SANs 1410 . Alternatively, the timing alignment information may be used by each SAN 1410 to adjust the timing of transmissions from each SAN 1410 such that the RF beam element signals 1411 from each SAN 1410 arrive at satellite 1408 aligned. used by FIG. 20 is an illustration of an optical transmitter 1460 having a timing module 1462 for adjusting the timing of beam element signals 1409 and timing pilot signals 1413 . Timing module 1462 receives timing control signals 1464 from satellite 1408 via a return downlink (discussed further below). The timing module applies appropriate delays to signals 1409 , 1413 to align signals transmitted by SAN 1410 with signals transmitted by other SANs 1410 in system 1400 .

In an alternative embodiment, timing adjustments may be made to the RF beam element signals 1411 within the satellite based on control signals generated by the satellite timing module 1417 . In some such embodiments, the control signal controls a programmable delay placed in the signal path between the optical receiver 1412 and the antenna array 1416 for each RF beam element signal 1411. .

In an alternative embodiment, at least two of the satellite timing signals 1415 are sent back to each SAN 1410 from the satellites. The first is a common satellite timing signal 1415 that is sent back to all SANs. That is, one of the received satellite timing signals 1415 is selected as the standard to which all others are to be aligned. The second is the satellite timing signal 1415 loopback. By comparing the common satellite timing signal 1415 to the loopback satellite timing signal 1415, each SAN 1410 aligns the two signals and thus the IF beam element signals 1418 from each SAN 1410 within the satellite 1410. can determine the amount of adjustment needed to

FIG. 21 is a system 1450 in which each of the K forward beam input signals 1452 contains S 500 MHz wide subchannels. In some embodiments, K=512 and S=7. For example, in some embodiments seven 500 MHz wide subchannels are transmitted in one user coverage area 1801 . FIG. 22 is an illustration of beamformer 1300 in which forward beam input signal 1452 includes seven 500 MHz wide subchannels, each coupled to a unique input to beamformer 1300 . Accordingly, as described above, the subchannels can be beamformed after being combined into an IF carrier, as shown in FIGS. Alternatively, as shown in FIGS. 14A, 13, subchannels 1452 can be beamformed using beamformer 1300 before being combined. Accordingly, beamformer 1300 outputs S×N beam element signals, and (S×N)/M such beam element signals are sent to respective SANs 1410 . In exemplary system 1450, S=7, N=512, and M=8. As noted above, these numbers are provided as a convenient example and are not intended to limit a system such as system 1450 to these particular values.

FIG. 22 is a simplified block diagram of a beamformer 1300 in which each carrier includes S subchannels 1452, where S=7. Each of subchannels 1452 is provided as an independent input to matrix multiplier 1301 within beamformer 1300 . Therefore, 512×7 subchannels 1452 are input to matrix multiplier 1301 . Here, 512 user spot beams are formed, and 7 is the number of subchannels within each carrier. That is, K=512 and S=7. A 512 path splitter 1304 receives each of the 512×7 subchannels 1407 , where 512 is the number of elements in the antenna array 1416 . Alternatively, N may be any number of antenna elements. Each subchannel 1452 is divided into 512 paths. Accordingly, 512×512×7 signals are output from divider 1304 in a three-dimensional matrix. Signals 1,1,1 to 1,K,1 (ie, 1,512,1 for K=512) are weighted and summed in weight and sum module 1306 . Similarly, signals 1,1,7 through 1,512,7 are weighted and summed in weight and sum module 1313 . In a similar manner, each of the other weighting and summing modules receives the weighted output from divider 1304 and weights and sums the same output. The 512×7 outputs from the weighting and summing modules 1306 , 1313 are coupled to the inputs of the timing module 1514 . The timing module functions essentially the same as timing module 1514 of beamformer 1406 discussed above. Beamformer 1300 outputs 512×7 beam element signals 1454 to SAN 1410 . Each of the eight SANs 1410 includes an IF combiner 1602 .

FIG. 23 is an illustration of SAN 1456 of system 1450 . In some embodiments, the first baseband-to-IF converter 805 operates in a manner similar to the baseband-to-IF converter 805 discussed above with respect to FIG. Transformer 805 outputs signal 811 which is a combination of seven 500 MHz beam element signals 1454 . Additionally, in some embodiments, at least one of the baseband to IF converters 1605 includes an additional frequency converter 1607 . Additional frequency translator 1607 receives timing pilot signal 1413 from beamformer 1300 . Timing pilot signal 1413 is combined with beam element subchannel 1452 and coupled to optical transmitter 607 . Each of the IF signals 811 coupled to the optical transmitters 607 are combined at the optical combiner 609 of each SAN 1410 to form the transmitted combined optical signal 1624 . Timing pilot signal 1413 is coupled to the input of frequency converter 1607 . Frequency translator 1607 places the timing pilot signal to a frequency that can be summed with beam element signal 1454 by summer 1608 . Alternatively, timing pilot signal 1413 can be directly coupled to an additional optical modulator 1610 dedicated to modulating timing pilot signal 1413 . The output of additional modulator 1610 is coupled to combiner 609 and combined with other signals on a unique optical channel dedicated to the timing pilot signal.

FIG. 24 is an illustration of the return link for system 1400 with terrestrial beamforming. User terminals 806 located within multiple of the 512 user beam coverage areas 1801 transmit RF signals to satellites 1408 . A 512-element antenna array 1902 (which may or may not be the same as antenna array 1416 ) on satellite 1408 receives RF signals from user terminal 806 . The 512/8 outputs from the 512 element antenna array 1902 are coupled to each of the eight amplifier/converter modules 1904 . That is, each element of antenna array 1902 is coupled to one LNA 1906 within one of amplifier/converter modules 1904 . The output of each LNA 1906 is coupled to the input to frequency converter 1908 and preamplifier 1910 . The amplified output of LNA 1906 is frequency downconverted from the RF user uplink frequency to IF. In some embodiments, the IF signal has a bandwidth of 3.5 GHz. In some embodiments, preamplifier 1910 provides additional gain prior to modulation onto the optical carrier. The output of each amplifier/converter module 1904 is coupled to a corresponding input to one of eight optical transmitters 1401, similar to optical transmitter 607 of FIG. Each of the eight optical transmitters 1401 outputs and transmits an optical signal to the corresponding SAN 1410 . SAN 1410 receives optical signals. SAN 1410 outputs 512/8 return beam element signals 1914 to downlink beamformer 1916 . A downlink beamformer 1916 processes the return beam element signals 1914 and outputs 512 beam signals 1918 each corresponding to one of the 512 user beam coverage areas 1801 .

Each IF signal provided from amplifier/converter module 1904 to optical transmitter 607 is coupled to one of 512/8 optical modulators 611 . For example, if there are 512 elements in antenna array 1902 (ie, N=512) and there are 8 SANs 1410 in system 1900, then 512/8=64. In a system, such as that shown in FIG. 9, where the IF signal is modulated onto wavelengths divided into four bands, the optical modulators 611 would include 512/(4×8) optical modulators 611. are grouped into optical band modules 608 having

Each optical modulator 611 is essentially the same as the uplink optical module 611 of SAN 1410 shown in FIG. 10 described above. Each optical modulator 611 within the same optical band module 608 has a light source 654 that produces an optical signal having one of 16 wavelengths λ. Correspondingly, the output of each optical modulator 611 has various wavelengths. Those optical signals generated within the same optical band module 608 will have wavelengths that are within the same optical band (i.e., for the case shown in FIG. 9, for example, the optical bands are 1100 nm, 1300 nm , 1550 nm, and 2100 nm). Each of those optical signals will be in one of 16 optical channels in a band based on wavelength λ2. The optical output from each optical modulator 611 is coupled to an optical combiner 609 . The output of optical combiner 609 is a combined optical signal that is transmitted to one of SANs 1410 via optical lens 2016 . Optical lens 2016 can be aimed at one of several SANs 1410 . Correspondingly, each of the eight optical transmitters transmits one of the eight optical signals to one of the eight SANs 1410 . A particular set of eight SANs can be selected from a larger group of candidate SANs depending on the quality of the optical link between the satellite and each candidate SAN.

FIG. 25 is an illustration of one of the SANs 1410 in the return link. Optical receiver 622 includes a lens 2102 that receives optical signals directed to SAN 1410 by lens 2016 from satellites. Optical band demultiplexer 2104 separates the optical signal into optical bands. For example, in some embodiments where there are four such bands, each of the four optical outputs 2106 are coupled to an optical channel demultiplexer 2108. Optical channel demultiplexer 2108 separates the 512/(4×8) signals combined in satellite 1408 . Each of the outputs from the four optical channel demultiplexers 2108 is coupled to a corresponding lens 2110 that focuses the optical output of the optical channel demultiplexer 2108 onto a photodetector, such as a photodiode 2112. . Each output signal 2116 from photodiode 2112 is coupled to one of the 512/8 LNAs 2114 . The output from each LNA 2114 is coupled to a return link beamformer 1916 (see Figure 24). Additionally, one channel output from the optical receiver 622 is essentially the SAN timing correction signal 1419 (see FIG. 18) provided by the satellite timing module to the return amplifier/converter module 1414 timing. A correction signal 1464 is output. In some embodiments, timing correction signal 1464 is coupled to timing pilot modem 2120 . The timing pilot modem outputs a signal 2122 that is sent to the forward beamformer 1406 . In other embodiments, the timing correction signal 1464 is coupled to the timing control input of the timing module 1462 (see FIG. 20) discussed above.

FIG. 26 illustrates in more detail the return beamformer 1916 according to some embodiments of the disclosed technology. Each of the 512 output signals 2116 is received from each of the SANs 1410 by a return beamformer 1916 . The return beamformer includes a beamformer input module 2203 , a timing module 2201 , a matrix multiplier 2200 and a beamformer output module 2205 . Matrix multiplier 2200 includes K-path splitting module 2202 and 512 weighting and summing modules 2204 . Matrix multiplier 2200 multiplies the vector of beam signals by a weighting matrix. Other arrangements, implementations, or configurations of matrix multiplier 2200 can be used. Each signal 2116 is received by beamformer 1916 at beamformer input module 2203 and coupled to timing module 2201 . Timing module 2201 ensures that any differences in path lengths and characteristics from satellite to SAN 1410 and from SAN 1410 to return beamformer 1916 are taken into account. In some embodiments, it transmits one pilot signal from the return beamformer 1916 to each SAN 1410 all the way to the satellite, and returns this pilot signal to the return beamformer 1916 via the SAN 1410. It may be done by The difference in path between the return beamformer 1916 and the satellite can be measured and taken into account.

The output of the timing module is coupled to a K-path divider 2202 that divides each signal into 512 identical signals. 512 unique signals are applied to each of the 512 weighting and summing circuits 2204 . Each of the 512 unique signals is weighted (i.e., phase and amplitude adjusted) in weighting circuit 2206 and then summed with the 512 other weighted signals in summation circuit 2208. , the return link user beam is formed at the output of the return beamformer.

Each of the architectures described above is shown for an optical uplink to a satellite. Additionally, the optical downlink from the satellite to the terrestrial SAN operates essentially inversely to the described optical uplink. For example, for the architecture shown in FIG. 4, an optical downlink from satellite 602 to SAN 604 provides a broadband downlink. Rather than lens 610 for receiving the optical uplink, a laser is provided for transmitting the optical downlink. Further, rather than the binary phase modulator 614 producing a BPSK modulated signal that is transmitted over an RF carrier, the binary phase modulator modulates the optical signal using an optical binary modulation scheme. Also, an optical downlink can be provided using an architecture similar to that shown in FIG. In this embodiment, modulator 614 is instead a QAM demodulator that receives a QAM modulated RF or IF signal, demodulates the bits of each symbol, and transforms the optical signal for transmission over the optical downlink. You will be using binary light modulation. In the architectural embodiment shown in FIG. 8, a similar architecture can be used where the feeder downlink from the satellite to the SAN is optical, and the received RF signals from the user terminals 842, 844 are A matrix switch directs the laser to the particular SAN that is selected to receive the signal. The RF signal is RF modulated onto the optical signal, similar to how the feeder uplink optical signal is RF modulated by baseband/RF modem 811 within SAN 802 .

In some embodiments, the lasers used to transmit optical feeder downlink signals are directed to one of several SANs. These SANs are selected based on the amount of signal fading in the light path from the satellite to each available SAN, similar to how the SANs of FIGS. 4, 8 and 12 are selected.

Although the disclosed technology is described above through various examples of embodiments and implementations, certain features, aspects, and functionality described in one or more of the individual embodiments may be , are not limited in their utility to the particular embodiments in which they are described. Accordingly, the breadth and scope of the claimed invention should not be limited by any of the examples provided in describing the above-disclosed embodiments.

The terms and phrases used in this document, and variations thereof, are to be interpreted as open-ended, as opposed to limiting, unless expressly stated otherwise. As an example of the foregoing, the term "including" shall be construed to mean "including without limitation" or the like; The term "example" is used to provide representative instances of the item under discussion and is not intended to provide an exhaustive or exclusive list thereof. shall be construed to mean "at least one," "one or more," or the like; , "traditional," "normal," "standard," "known," and terms of similar import refer to the item being described. should not be taken to be limited to items available at any given time period or at any given time, but instead to items that may be available now or in the future, conventional, traditional, customary, or should be construed to encompass standard techniques. Similarly, when this document refers to technologies that would be apparent or known to those of ordinary skill in the art, such technologies encompass technologies that are now or in the future apparent or known to those of ordinary skill in the art.

A group of items joined by the conjunction "and" should not be construed as requiring that each and every one of those items be present in the group, but rather explicitly stated otherwise. shall be construed as "and/or" unless otherwise specified. Similarly, a group of items joined by the conjunctive "or" should not be construed as requiring mutual exclusion within the group, but rather not explicitly stated otherwise. As far as possible, it should still be construed as "and/or." Furthermore, although any item, element, or component of the disclosed technology may be described or claimed in the singular, the plural is within its scope unless the singular is explicitly stated. is assumed.

breadth, such as "one or more," "at least," "but not limited to," or other similar phrases in some instances The presence of a broadening word or phrase shall not be construed to mean that a narrower instance is intended or required in the absence of such broadening phrase. The use of the term "module" does not imply that all of the components or functionality described or claimed as part of the module are arranged in a common package. In fact, any or all of the various components of the module, whether control logic or other components, may be combined in a single package or maintained separately, and multiple can be further arranged in groups or packages of or across multiple locations.

Additionally, various embodiments described herein are described with reference to block diagrams, flow diagrams, and other illustrations. As will be apparent to one of ordinary skill in the art after reading this document, the illustrated embodiments and their various alternatives can be implemented without being limited to the illustrated examples. For example, block diagrams and their accompanying descriptions should not be construed as implying a particular architecture or configuration.

Claims (50)

an optical receiver having multiple digital outputs;
a plurality of radio frequency modulators having digital inputs and analog outputs, the digital inputs being coupled to one of the plurality of digital outputs of the optical receiver;
A beamformer having a plurality of beamformer inputs coupled to corresponding ones of said analog outputs, wherein the number of beamformer inputs is the number of user spot beams formed by said beamformer. a beamformer equal to the number, said beamformer further comprising a plurality of beamformer outputs;
an antenna array having a plurality of antenna elements, each antenna element having an input coupled to a corresponding one of said beamformer outputs. an optical receiver having multiple radio frequency (RF) outputs;
A beamformer having a plurality of beamformer inputs coupled to corresponding ones of said RF outputs, wherein the number of beamformer inputs is the number of user spot beams formed by said beamformer. a beamformer equal to the number, said beamformer further comprising a plurality of beamformer outputs;
an antenna array having a plurality of antenna elements, each antenna element having an input coupled to a corresponding one of said beamformer outputs. 2. The satellite of claim 1, further comprising a plurality of LNAs, each LNA coupled between one of said plurality of modulators and a corresponding one of said beamformer inputs. Antenna patterns of at least some of said antenna elements overlap such that signals transmitted therefrom are superimposed on top of each other and thus coherently combined to form a user spot beam. 3. A satellite according to item 1 or 2. 5. The satellite of claim 4, wherein the user spot beams are directed to a user beam coverage area distributed over a satellite service coverage area substantially larger than the user beam coverage area. 4. A satellite according to claim 2 or 3, wherein the optical receiver comprises an optical demultiplexer having an input and a plurality of outputs, each output associated with a corresponding optical wavelength. 7. The satellite of claim 6, wherein the wavelengths associated with the outputs of the optical demultiplexers are grouped into optical bands. 8. The satellite of claim 7, wherein wavelengths within the same optical band define unique optical channels. 3. A satellite according to claim 1 or 2, wherein the optical receiver comprises a plurality of satellite receiver photodetectors each having a digital output coupled to a corresponding digital output of the optical receiver. Each satellite receiver photodetector has an optical input and the digital output has two logic states, the first logic state being above the first intensity level. , a received optical signal coupled to an input of said satellite receiver photodetector, and a second logical state is associated with said signal being below a second intensity level. 10. A satellite according to claim 9. 2. The satellite of claim 1, wherein said modulator is a binary phase modulator. 2. The satellite of claim 1, wherein said modulator is a QAM modulator. 3. The satellite of claim 1 or 2, further comprising at least one frequency converter coupled between corresponding beamformer outputs and corresponding antenna element inputs. 14. The satellite of claim 13, further comprising a power amplifier coupled between the output of the frequency converter and the corresponding antenna element input. 2. The method of claim 1, further comprising a plurality of optical receivers, each having a plurality of optical receiver outputs, each optical receiver output coupled to a corresponding digital input of a modulator. satellite. an additional beamformer and an additional optical receiver, each additional optical receiver having a plurality of digital outputs, the additional beamformer being an analog of the additional optical receiver; a plurality of beamformer inputs coupled to corresponding ones of the outputs, the number of beamformer inputs being equal to the number of user spot beams formed by said beamformer; The device further has a plurality of beamformer outputs, the number of beamformer outputs from each additional beamformer being dependent on the number of beam element signals used to form one user spot beam. 2. A satellite according to claim 1, which is equal. In the system
an optical transmitter including a plurality of optical modulators, each optical modulator having a radio frequency (RF) input and an optical output;
an optical combiner having a plurality of inputs, each input coupled to the optical output of a corresponding one of the plurality of optical modulators;
a lens;
at least one satellite access node (SAN) comprising
an optical receiver having multiple radio frequency (RF) outputs;
A beamformer having a plurality of beamformer inputs coupled to corresponding ones of said RF outputs, wherein the number of beamformer inputs is the number of user spot beams formed by said beamformer. a beamformer equal to the number, said beamformer further comprising a plurality of beamformer outputs;
an antenna array having a plurality of antenna elements, each antenna element having an input coupled to a corresponding one of said beamformer outputs;
A system comprising a satellite comprising: Antenna patterns of at least some of said antenna elements overlap such that signals transmitted therefrom are superimposed on top of each other and thus coherently combined to form a user spot beam. Item 18. The system according to Item 17. 19. The system of claim 18, wherein the user spot beams are directed to a user beam coverage area distributed over a satellite service coverage area substantially larger than the user beam coverage area. an optical transmitter including a plurality of optical modulators, each optical modulator having an electrical input and an optical output;
an optical combiner having a plurality of inputs, each input coupled to the optical output of a corresponding one of the plurality of optical modulators;
at least one satellite access node (SAN), including a lens;
at least one optical receiver configured to receive an optical signal from said optical transmitter, said optical receiver having a plurality of digital outputs;
A plurality of radio frequency (RF) modulators having digital inputs and analog outputs, wherein the digital inputs are coupled to one of the plurality of digital outputs of the optical receiver. a modulator;
A beamformer having a plurality of beamformer inputs coupled to corresponding ones of said analog outputs, wherein the number of beamformer inputs is the number of user spot beams formed by said beamformer. a beamformer equal to the number, said beamformer further comprising a plurality of beamformer outputs;
an antenna array having a plurality of antenna elements, each antenna element having an input coupled to a corresponding one of said beamformer outputs; A satellite communication system. 21. A system according to claim 19 or 20, wherein the optical receiver comprises an optical demultiplexer having an input and a plurality of outputs, each output associated with a corresponding optical wavelength. 22. The system of claim 21, wherein the wavelengths associated with the outputs of the optical demultiplexers are grouped into optical bands. 18. The system of claim 17, wherein the optical receiver includes a plurality of satellite receiver photodetectors each having an RF output coupled to a corresponding RF output of the optical receiver. 24. The system of claim 23, wherein each optical receiver further includes a steerable lens having an output coupled to said input of at least one of said plurality of satellite receiver optical detectors. 21. The system of claim 17 or 20, further comprising at least one frequency converter coupled between a corresponding one of said beamformer outputs and a corresponding one of said antenna element inputs. 26. The system of Claim 25, further comprising a power amplifier coupled between an output of one of said plurality of frequency converters and a corresponding one of said antenna element inputs. 4. The antenna patterns of at least some of said antenna elements overlap such that the signals transmitted therefrom are superimposed on top of each other and coherently combined to form a user spot beam. 21. The system according to 20. 21. The system of claim 20, wherein said user spot beam is directed to a user beam coverage area. 29. The system of claim 28, wherein the user spot beams are directed to a user beam coverage area distributed over a satellite service coverage area substantially larger than the user beam coverage area. 21. The system of claim 20, wherein the optical receiver includes a plurality of satellite receiver photodetectors each having a digital output coupled to a corresponding digital output of the optical receiver. Each satellite receiver photodetector has an optical input and the digital output has two logic states, the first logic state being above the first intensity level. , a received optical signal coupled to an input of said satellite receiver photodetector, and a second logical state is associated with said signal being below a second intensity level. 31. The system of claim 30. 3. The satellite of claim 2, further comprising a plurality of low noise amplifiers (LNAs), each coupled between an optical receiver output and a corresponding beamformer input. 3. The satellite of claim 2, wherein said RF signal output from said satellite receiver detector has an amplitude that tracks said intensity of said optical signal applied to said satellite receiver detector input. 34. The satellite of claim 33, wherein each optical receiver further comprises a steerable lens having an output coupled to said input of at least one of said plurality of satellite receiver optical detectors. 35. The satellite of claim 34, wherein the steerable lens is positionable by rotation about at least two axes in response to ground commands. 35. The satellite of Claim 34, wherein said steerable lens is positionable by rotation about at least two axes in response to on-board processing. 34. The satellite of claim 33, wherein said satellite receiver photodetector is a photodiode. 3. The satellite of claim 2, further comprising a plurality of optical receivers, each having a plurality of optical receiver outputs, each optical receiver output coupled to a beamformer input. A method of transmitting information via a satellite in a satellite communication system comprising:
receiving an optical signal within a satellite;
Demultiplexing the optical signals to output a plurality of demultiplexed optical signals, each of the plurality of demultiplexed optical signals having a wavelength within a unique optical channel. and,
generating a plurality of analog electrical signals, each having an amplitude determined according to the optical intensity of one of the demultiplexed optical signals;
applying the plurality of analog electrical signals to a beamformer on board the satellite;
receiving beam element signals from the beamformer;
and C. transmitting said beam element signals from an antenna array such that said beam element signals form user spot beams when they overlap each other. receiving commands in the beamformer to generate beam element signals, each of the beam element signals being responsive to the quality of the optical link between a satellite access node (SAN) and the satellite; 40. The method of claim 39, wherein the beams are weighted to form user spot beams directed to the first user beam coverage area based on. wherein the received commands include commands to generate beam element signals, each of the beam element signals being user spot beams directed to a first user beam coverage area during a first period of time; 41. The method of claim 40, wherein the beam is weighted to form a user spot beam directed to a second user beam coverage area during the second time period to form a . 40. The method of Claim 39, further comprising amplifying the beam element signals prior to transmission. an antenna having multiple antenna outputs;
a plurality of frequency converters, each coupled to a corresponding one of the plurality of antenna outputs;
a beamformer having a plurality of beamformer inputs and beamformer outputs, each beamformer input coupled to a corresponding one of said frequency converters;
A plurality of radio frequency (RF) demodulators, each having an RF demodulator input configured to receive an RF signal from a corresponding beamformer output and outputting a digital data stream a plurality of RF demodulators configured to;
Optical having multiplexed optical channels having a plurality of digital inputs, each coupled to the output of a corresponding one of said RF demodulators, and onto which said digital data stream is modulated an optical transmitter having an optical output configured to output a signal. 44. The satellite of claim 43, wherein said RF demodulator is a binary demodulator. 44. The satellite of claim 43, wherein said RF demodulator is a QAM demodulator. an antenna having multiple antenna outputs;
a plurality of frequency converters, each having a converter input coupled to a corresponding one of said antenna outputs and having a converter output;
A beamformer having a plurality of beamformer inputs and beamformer outputs, wherein each of said beamformer inputs is coupled to a corresponding output of one of said plurality of frequency converters. a former;
An optical transmitter having a plurality of radio frequency (RF) inputs each coupled to a corresponding beamformer output and having an optical output, the optical output coupled to the RF input an optical transmitter configured to output an optical signal having multiplexed optical channels modulated by the signal being transmitted. an antenna having multiple antenna outputs;
a plurality of frequency converters, each coupled to a corresponding one of the plurality of antenna outputs;
a beamformer having a plurality of beamformer inputs and beamformer outputs, each beamformer input coupled to a corresponding one of said frequency converters;
A plurality of radio frequency (RF) demodulators, each having an RF demodulator input configured to receive an RF signal from a corresponding beamformer output and outputting a digital data stream a plurality of RF demodulators configured to;
Optical having multiplexed optical channels having a plurality of digital inputs, each coupled to the output of a corresponding one of said RF demodulators, and onto which said digital data stream is modulated an optical transmitter having an optical output configured to output a signal; and a satellite.
a steerable optical lens configured to receive optical signals from the satellite;
a demultiplexer input coupled to receive the optical signal from the optical lens; and a plurality of demultiplexer outputs configured to output optical channels demultiplexed from the optical signal. and an optical demultiplexer having
A plurality of photodetectors, each photodetector coupled to a corresponding one of said demultiplexer outputs, said photodetector having a detector output. a satellite access node (SAN) comprising: a satellite access node (SAN); 48. The satellite communication system of Claim 47, wherein said detector output is configured to output a digital data stream. wherein the detector output is configured to output an RF signal, the amplitude of the RF signal being equal to the amplitude of the signal coupled to the detector from the corresponding one of the demultiplexer outputs; 48. A satellite communication system according to claim 47, proportional to intensity. an antenna having multiple antenna outputs;
a plurality of frequency converters, each having a converter input coupled to a corresponding one of said antenna outputs and having a converter output;
A beamformer having a plurality of beamformer inputs and beamformer outputs, wherein each of said beamformer inputs is coupled to a corresponding output of one of said plurality of frequency converters. a former;
An optical transmitter having a plurality of radio frequency (RF) inputs each coupled to a corresponding beamformer output and having an optical output, the optical output coupled to the RF input an optical transmitter configured to output an optical signal having multiplexed optical channels modulated by the signal being transmitted;
a steerable optical lens configured to receive optical signals from the satellite;
a demultiplexer input coupled to receive the optical signal from the optical lens; and a plurality of demultiplexer outputs configured to output optical channels demultiplexed from the optical signal. and an optical demultiplexer having
A plurality of photodetectors, each photodetector coupled to a corresponding one of said demultiplexer outputs, said photodetector having a detector output. a satellite access node (SAN) comprising: a satellite access node (SAN);

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